Japanese Patent Publication No. 2009-25338 describes detecting the peripheral brightness of a projector, and adjusting the brightness of an image in accordance with the peripheral brightness. More specifically, a method whereby the luminance of an image is determined in accordance with the peripheral illuminance using a luminance specification table, and a method whereby the luminance of an image is determined by carrying out a calculation in accordance with the peripheral illuminance, are described in Japanese Patent Publication No. 2009-25338.
However, with these kinds of method, it can be supposed that the brightness of the image fluctuates due to reacting too sensitively to a change in the peripheral illuminance. For example, the brightness of the image fluctuates when someone passes in front of an illuminance sensor, when the door of a dark room opens, and the like. Also, in the case of the method using the table, when the illuminance is around the threshold value of the table, the brightness of the image fluctuates every time the illuminance is measured. In particular, when the illuminance sensor and an operating button, or the like, are disposed adjacent to each other, the illuminance sensor measurement value fluctuates during an operation, meaning that the brightness of the image is liable to fluctuate.